5D Supersymmetric Orbifolds: Supergravity/Phenomenological Aspects

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Abstract

Five-dimensional braneworlds attracted much attention in recent years, be it for phenomenological, cosmological or theoretical reasons. In this work we study supersymmetric theories compactified on the orbifold S1/Z2. We start with a short discussion of power-law unification, where 5D rigid super Yang-Mills theory is introduced in its superfield formulation. We develop a superfield description of 5D orbifold N = 2 supergravity coupled to vector and hyper multiplets. The basic building blocks are N = 1 supermultiplets obtained as reductions of the full multiplets of N = 2 conformal supersymmetry by Fujita, Kugo and Ohashi. After identifying the relevant superfields we build superspace actions for the vector, hyper and radion sectors. The couplings of these sectors to the 4D Weyl multiplet are obtained by the replacement of integrations over (flat) superspace by the F and D densities of 4D conformal supergravity. We then observe that a Weyl rescaling is enough to extend the formalism to warped geometries, and show how to consistently introduce brane-localized couplings. The superfield approach to 5D orbifold N = 2 supergravity is used to rederive the BPS conditions in the generalized Randall-Sundrum models without using the 4-form mechanism to introduce the odd couplings. It is noted that BPS conditions correspond to F and D flatness conditions, which are simple to obtain in this formalism. Next, a study of recent claims on supersymmetric radion stabilization leads us to speculate on a possible no-go theorem on this possibility. We then consider the supergravity embedding of tuned Fayet-Iliopoulos terms, show that they do not break supersymmetry even in warped geometries, and obtain new supersymmetric vacua with negative brane tensions and a bulk fat brane. We close with a study of supersymmetric models of gauge inflation.